It could mean a story where a wife made a mistake or had a slip - up. Maybe she accidentally revealed a secret, or made an error in judgment in a particular situation.
Here's an example. A wife was chatting with her neighbor and slipped up by revealing some personal financial problems her family was having. Her husband had wanted to keep those issues private. As a result, there was some tension between the husband and wife as he was disappointed that she had let that information out. This kind of story shows how a wife's slip - up can have consequences on relationships and family dynamics.
Well, perhaps it refers to an object or an event. Say, a small memory or an item that unexpectedly found its way into the story about his wife while he was telling it. It might be something like a little joke that he didn't plan on saying but just came out as part of the story.
For instance, he was recounting a story of their vacation. He was focused on how his wife loved the beach. But then, accidentally, he slipped in that she got a little scared when she saw a big crab. So, the incident of her getting scared by the crab was the 'it' that found its way into the story about his wife.
It could mean he secretly introduced something (like an idea or a small object) into the stories about your wife. Maybe he added a false detail or a new element without permission.
First, you should find out exactly what 'it' is. If it's something inappropriate or false, you can calmly correct the person and set the record straight.
First, make sure your neighbor is okay physically. Then, depending on what your wife's story is about, you might need to clarify things. If it's a misunderstanding, calmly explain the real situation to your neighbor.
If we consider 'it slipped into mom story', it could be that there was a certain object or concept that got incorporated into a story centered around mom by accident or without much thought. Let's say a story was being told about mom's cooking, and suddenly a story about a kitchen gadget that she used once'slipped into' the cooking story. It might have been added because it was related in some way, like it helped her cook better, or it could have been just a random association that the storyteller made while talking.
This phrase is very difficult to interpret without more context. 'Cock' could refer to a rooster perhaps in a very strange context related to a'spooning story' which might be about people lying closely together like spoons. But it's all very ambiguous.